To validate utility of the equivalent circuit of Figure 2(a), the maximum frequency for the junction transistor at which their amplification is unity, being dependent somewhat upon the DC collector voltage
, was assumed by Giacoletto as
Digital Display Monitors: Collector Current, Collector Voltage
, Helix Current, Helix Voltage, Forward RF Power, Reflected RF Power, Filament Hours, Beam Hours
After the first base current is set, the collector voltage
is swept while the collector current is measured.
In class B operation, which is a special case of class C with a conduction angle of half a period, the collector voltage
waveform is pure sinusoidal and harmonics are present in the collector current only.
Figure 4 shows the collector voltage
and current waveforms.
The HBT breakdown voltage is over 20 V for [BV.sub.cbo] and over 10 V for [BV.sub.ceo] Therefore, the amplifier can operate at higher than 5 V collector voltage
. However, the ESD protection circuitry limits the collector voltage
to approximately 12 V, which means [V.sub.cc] is limited to 7 V to avoid the kick-on of the ESD protection.
Standard features include a built-in IEEE-488 (GPIB) inter-face, 0 dBm input for rated output, gain control, RF output sample port, VSWR protection for the TWT only (not required for the solid-state unit), plus monitoring of the TWT helix current, cathode voltage, collector voltage
, heater current, heater voltage, base-plate and cabinet temperature.
As beta increases, the collector current increases, causing the voltage drop across the external collector resistor to increase with an associated reduction of collector voltage
. Dropping the collector voltage
causes the collector current to decrease.
[f.sub.T] and [f.sub.max] are highly dependent on the transistor layer design and are functions of collector voltage
and collector current density.
For collectors, the determining parameters are power dissipation, cooling fluid choice, collector voltage
and the number of stages, as listed in Table 4.